The present invention relates to industrial robots, or more particularly to an industrial robot hand useful for the transportation of integrated circuit wafers. Typically, an industrial robot has an articulated mechanical arm, on the end of which is a "hand". The arm and hand movements are controlled by a servosystem which directs the hand to accomplish any desired pattern of movements. Through programming the robot is directed through various movements in a desired sequence. The use of a sensor input provides the robot with a knowledge of the changes to its environment, i.e. intrusions. Robot control algorithms may monitor sensor states to make decisions concerning the suitability of certain actions.
The manufacture of integrated circuits is becoming a highly automated process. Semiconductor wafers are processed with wafers held in carriers containing twenty-five wafers each. Processing the wafers requires handling and manipulation of the wafer carriers for transporting the wafers between process steps and loading wafer carriers into process machines. The process machines may produce corrosive fumes and liquids which may contact and attack any handling surface.
The wafers are extremely fragile and may be of very high monetary value. For this reason, handling techniques must be very reliable and done in a manner to protect the wafer carriers from being dropped, or forcefully crushed. When handling tasks are given to robots, the robot must be given the ability to sense and judge the safety of its load.
Wafer handling is becoming automated, that is, robots are being introduced to manipulate the carriers through the process steps. Robotic handling of wafer carriers is relatively new and suffers from the inability to determine whether the carrier grasp by the robot arm is successful and the inability to detect a collision during motion of wafer carriers. Detecting collisions during motion affords a peripheral benefit of improving the safety of people and adjacent equipment which may be damaged by a non-sensing robot.
This invention solves the foregoing problems of robotic wafer carrier handling by providing mechanical engagement of the wafer carriers in such a manner that a sensor is able to detect when the carrier position is correct for safe lifting of the wafer carrier, thus allowing the robot to decide whether movement is appropriate. The grasp mechanism is mounted to the robot arm in a manner enabling detection of a collision and halting further motion attempts. This prevents damage to the wafer carrier payload, robot mechanisms and the encountered object.
Typically, grippers available from robot arm manufacturers are successful in grasping a wafer carrier that is properly presented and which does not exhibit wear or distortion. This works well if the wafer carriers are accurately placed and the grasped carrier remains securely in the gripper.
In practice, manipulation may be unreliable, limited by carrier distortion and accuracy limitations of the machine delivering the wafer carrier. When delivery deviations occur beyond the acceptance limits of the gripper, it may either miss the wafer carrier entirely, causing the downstream process machine to deal with an error condition, or the gripper may make a partial grip, causing distortion or damage to the wafer carrier, crushed wafers or a dropped wafer carrier.
Similarly, wafer carriers which are worn or otherwise distorted from original design dimensions may cause mis-grip problems when a non-sensing gripper is utilized. As above, the results are distortion or damage to the wafer carrier when the carrier slips out during movements. The carrier is also subject to entanglement at the pick-up position and may encounter foreign objects in its path of motion. Also, mis-programming or hardware failure could cause a collision path to be followed. In these cases, the carrier may be wrenched from the gripper or the carrier may be crushed between the gripper and the obstacle.
Existing wafer carrier handling end effectors are deficient in having no qualitative feedback to the robot controller to allow judgment on the success of the grasp attempt as well as the security of the carrier after it is in the gripper and in motion. The invention provides workpiece sensing and lifting, as well as collision sensing. In the event of a misgrip, the invention provides error recovery in that the robot may be programmed to make minute movements and search for proper grip before giving up on the grip attempt.